Magnetic recording-reproducing device



3 F. G. BUHRENDORF MAGNETIC RECORDING-REPRODUCING DEVICE Filed Aug. 26,1952 INVENTOR F. G. BUHRENDORF A TTORNEV Patented Nov. 3, 1953 UNITEDSTATES ?ATENT' @FFICE 2,658,114 MAGNETiC RECORDING-REPRODUCING DEVICEFrederick G. Buhrendorf, Westfield, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkAp lication August 26, 1952, Serial N0. 306,423

11 Claims. -1

This invention relates to electromagnetic transducers, and particularlyto an electromagnetic transducer with a transformer built therein toform a single unitary structure.

An object of this invention is to provide an economical, high frequencymagnetic recordingreproducing device comprising a plurality ofindependently operative, accurately spaced recording-reproducingelements disposed in close proximity.

Another object of this invention is to provide a high frequency magneticrecording-reproducing device comprising two independently operativerecording=reproducing elements disposed in such close proximity as to becapable of successively scanning each of a plurality of spots recordedon a track of a magnetic record medium one spot at a time, the spacebetween said elements being substantially less than the distance, centerto center, between adjacent recorded spots.

In accordance with this invention the abovenoted requirements aresatisfactorily met by a novel electromagnetic transducer which comprisestwo transformer cores joined together by a bridge member to form aunitary structure. A surface of the bridge member faces the magnetizablesurface of the record medium and the independently operative recordingreprodu'cing elements are disposed in a portion of said bridge membersurface which is substantially flat and parallel to the magnetizablesurface of the record medium. Each core carries two windings. Theprimary winding, which is to be connected to the associated equipment,consists of a convenient number of turns of insulated wire, such asenamel covered copper wire, the number of turns being defined by theassociated equipment and the structural limitations of the core. 'Thesecondary winding is endless and consists of one or several turnsterminated in a slender filament of conducting material disposed in aslot or groove in the substantially flat portion of the surface of thebridge member which faces the magnetizable surface of the record medium.Flux surrounding this filament, when current is induced in it, is usedto record on the magnetic medium in much the same manner as inconventional airgap type heads. In reproduction, current induced in thisfilament generates a flux in the core and, by virtue of the transformeraction, a voltage is delivered to the associated equipment by the largerprimary winding. Each of the secondary windings is applied directly tothe surface of its related core and. the recording-reproducing elements,or operating filaments are spaced, center to center, as little as 0.005inch apart, a spacing which is impracticable, if not impossible, with aconventional gap type structure.

The nature of the invention and its distinguishing features andadvantages will be more clearly understood from the following detaileddescription and the accompanying drawings in which:

Fig. 1 is a plan view of an embodiment of the present invention in whicheach of the secondary windings is a single turn;

Fig. 2 is a view in perspective of the secondary windings shown in Fig.i; I A

Fig. 3 is a partial enlarged plan view of the embodiment of Fig. 1 inthe region of the confronting secondary windings and the closely spacedgrooves in which aredisp'osed the filamentary portions of said windings;and

i Fig. i is a plan view showing the actual dimensions of anelectromagnetic transducer in accorolance with the present invention.- I

Referring now to the accompanying drawings, 2 is a core of theelectromagnetic transducer and is preferably made of a high permeability-low loss, magnetic material, such as; ferrite. The bridge member tjoins the cores 2 and, in order to facilitate the manufacture of aunitary structure, may be of the same magnetic material as cores 2; Inthe particular embodiment of this invention shown in Figs. 1 to 4 theouter surface 6 of the bridge member is tangential to the peripheralsurfaces of the cores, and the portion 8 of surface 6 between the linesA and B is substantially flat and parallel to the magnetizablesurface ofthe record medium which it faces. Each of the endless secondary windingsI0 consists of one turn of a low resistance material, such as, copper orsilver, and is terminated in a slender filament of low resistance,conducting material I2 which is disposed in one of the parallel slots orgrooves M in the substantially flat portion 8 of the bridge menac-serrate 6. For optimum results, the filament 12 should be flush withthe fiat surface 8. It is to be understood that the endlesssecondarywinding that sist of a blurality of turns terminated in a meet, such as,the filament l2 showii in Figsl to 4; er the primary windings Itcomprises t imming; of turns of insulated low resistance wire, such as,enamel covered wire, wound in such manner as to be coupled closely tothe core and its relate secondary winding, and to terminate in the wires18. 20 and 22, 24, respectively. The number pf ttirhS in each of thesewindings is defined by the asseciated equipment to they are "to beconnected and the Structural limitations er the core.

While satisfactory results may be'obtained with transducers inaccordance with the present -invention in which the filaments :lie at anangle with respect to the axes of the cores-it has been found that forconvenience manufacture and simplicity in mounting, the filamentsshouldbe disposed in suchmanner as to be parallelto each other and to the axesof the 'cores shown in Fig. 2. ,th

For optimum results the filaments should lie in a plane substantiallyparallel to the magnetizable surface of the record medium, and should bedisposed normal to the direction of the relative motion of thetransducer with respect to the record medium.

The particular embodiment of this invention as shown in Figs. 1 to 4 isintended for use with a, right circular cylindrical record mediumrevolving about its axis. The transducer is disposed so that eachfilament clears the magnetizable surface of the record medium bysubstantially 0.002 inch and is parallel to the axis of the cylindricalrecord medium. The filaments H are substantially 0.002 inch in width;the flat surface 8 as shown between the lines A and B in Figs. 1 to 3 issubstantially 0.031 inch in length; and the secondary windings I aredisposed with respect to each other at an angle C of substantially 60degrees.

The conductor of the secondary winding should have as large across-section as possible, the area of said cross-section being limitedonly by the distributed capacity in a turn of the winding. The optimumaverage width of the conductor of the secondary winding is equal tosubstantially one tenth the average length of the magnetic path in itsrelated core.

In the preparation of the transducer, the secondary windings may beapplied directly to the surfaces of the cores 2 in the manner describedin applicant's patent application, Serial No. 262,950, filed December22, 1951.

By using one of the two filaments for reading and the other for writingit is possible to read in advance of recording by as little as of a celltime (a cell is equal to the distance, center to center, betweenadjacent recorded spots).

By spacing the filaments the exact multiple of cell size (as little asone or two or perhaps as much as or times) required to span an entry tobe recorded, and again using one filament for recording and the otherfor reading, it is possible to repeat continuously the operations ofrecording and reading the entry so as to make the recorded entryavailable for reading in a small fraction of the time required to rotatethe drum a full revolution.

It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Other arrangements may be devised by those skilled in the art, withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. An electromagnetic transducer comprising a pair of transformer cores,a bridge member joining said cores to form a unitary structure, a pairof grooves in said bridge member, a first winding on each of said cores,said windings being endless, a second winding on each of said cores,each of said endless windings including a segment individually disposedin one of said grooves.

2. An electromagnetic transducer comprising a pair of transformer cores,a bridge member joining said cores to form a unitary structure, saidbridge member having an outer surface, a pair of grooves in said outersurface of said bridge member, a first winding on each of said cores,said windings being endless, a second Winding on each of said cores,each of said first windings including a segment individually disposed inone of said grooves.

3. An electromagnetic transducer in accord- .4 ance with claim 2 whereineach of said segments of said endless windings is filamentary.

4. An electromagnetic transducer in accordance with claim 2 wherein saidsegments of said endless windings are disposed in said grooves in suchmanner as to be fiush with the outer surface of said bridge member.

5. An electromagnetic transducer in accordance with claim 2 wherein eachof said endless windings consists of a single turn.

6. An electromagnetic transducer in accordance with claim 2 wherein eachof said endless windings consists of a plurality of turns.

7. An electromagnetic transducer in accordance with claim 2 wherein saidsegments of said endless windings are parallel.

8. A magnetic recording or reproducing system including a record mediumhaving a magnetizable surface, an electromagnetic transducer and meansfor providing relative motion between said record medium and saidtransducer, wherein said transducer comprises a pair of transformercores, a bridge member joining said cores to form a unitary structure,said bridge member having a surface which faces the magnetizable surfaceof said record medium, a portion of said surface of said bridge memberbeing substantially parallel to the magnetizable surface of said recordmedium, a pair of grooves in said portion of said surface of said bridgemember, a first winding on each of said cores, said windings beingendless, a second winding on each of said cores, each of said firstwindings including a segment individually disposed in one of saidgrooves.

9. A magnetic recording or reproducing system in accordance with claim 8wherein said segments of the endless windings of said electromagnetictransducer are disposed normal to the direction of the relative motionbetween I said transducer and said record medium.

10. An electromagnetic transducer comprising a pair of toroidaltransformer cores, a tangential bridge member joining said cores to forma unitary structure, said bridge member having an outer surface which istangential to the peripheral faces of said cores, a pair of grooves insaid outer surface of said bridge member, a first winding on each ofsaid cores, said windings being endless, a second winding on each ofsaid cores, each of said first windings including a segment individuallydisposed in one of said grooves.

11. A magnetic recording or reproducing system including a record mediumhaving a magnetizable surface, an electromagnetic transducer and meansfor providing relative motion between said record medium and saidtransducer, wherein said transducer comprises a pair of toroidaltransformer cores, a tangential bridge member joining said cores to forma unitary structure, said bridge member having an outer surface which istangential to the peripheral surfaces of said cores and which faces themagnetizable surface of said record medium, a portion of said outersurface of said bridge member being substantially fiat and parallel tothe magnetizable surfaces of said record medium, a pair of grooves insaid substantially fiat portion of said outer surface of said bridgemember, a first winding on each of said cores, said windings beingendless, a second winding on each of said cores, each of said firstwindings including a segment individually disposed in one of saidgrooves.

FREDERICK G. BUHRENDORF.

No references cited.

